1. Field of the Invention
The present invention relates to a cytological sampling instrument for collecting cells exfoliated from the uterine cervix.
2. Brief Description of the Prior Art Drawings
FIGS. 1, 2, 3 and 4 are corresponding, somewhat diagrammatic, generally axial sections through a vaginal cavity showing in elevation the most popular prior art cytological sampling instruments currently in use.
3. Prior Art
In each of the known cervical cytological sampling methods the object is to collect a large number of cells that originated at the uterine cervix and, to a lesser degree, at the uterus, to be deposited on a slide and "fixed" by application of fixative for preservation of the cells. After suitable processing, subsequent microscopic examination in a medical laboratory reveals whether or not abnormal cells are present which are indicative of cancer or lesions accepted as being precursors of cancer.
As illustrated in FIG. 1, in one method the vagina 1 is distended by a speculum 2 enabling the portio vaginalis (vaginal portion) 11 of the cervix to be viewed, and a paddle-like scraper 3 is used to collect exfoliated cells from the posterior fornix 4 of the vagina, that is, from the "vaginal pool". This is the area selected for sampling by Papanicolaou because cells exfoliated from virtually all areas of the cervix and from the uterus gather in the vaginal pool, though Papanicolaou proposed sampling this region by aspiration. Unfortunately, however, cells begin deteriorating immediately upon exfoliation to the point where at least a large proportion of the cells obtained in a vaginal pool smear have little or no diagnostic value. In addition, while large numbers of cells usually are obtained, the origins of the cells present in the vaginal pool at any given moment are not known so that there is no assurance that cells from areas prone to cancer will be obtained. It is now recognized that a false negative rate of about 50% can be expected for vaginal pool smears, that is, even after examination about one-half of the cases of invasive cervical cancer and cervical intraepithelial neoplasia ("CIN") remain undetected. Nevertheless, since vaginal pool smears are quickly, easily and inexpensively taken, they still are used to a large extent, particularly when funds for screening a large population are limited.
As early as 1947, the year in which the application resulting in Ayre U.S. Pat. No. 2,471,088 was filed, it was recognized that the vast majority of lesions resulting in invasive cervical cancer originate at the undulating circumferential border 5 between the squamous cells of the ectocervical epithelium 17 and the columnar cells of endocervical epithelium 18, which border is referred to as the squamo-columnar junction, the transformation zone or the "T-zone". Though the T-zone is variously located in different women, usually it is at or closely adjacent to the external os 6. It is extremely important that cells from this area be present in a sample.
Ayre invented the specially designed scraper 7 shown in FIG. 2 to be used for scraping the entire circumferential extent of the T-zone for early detection of cell abnormalities. In general, the Ayre scraper has two lobes including a frontal lobe 8 insertable slightly into the endocervical canal 9 and an adjacent lateral lobe 10 abuttable against the vaginal portion or ring 11 of the cervix. The frontal lobe 8 acts as a pivot as the scraper is rotated for scraping of the entire circumferential extent of the T-zone.
Ayre, himself, recognized that a more reliable diagnosis could be obtained if the scraping sample was not the only sample obtained from a patient. He proposed that at least two separate sampling operations be performed--one using his scraper and another using a separate instrument for obtaining an additional sample directly from the endocervical canal. In fact, research has shown that relying solely on a sample obtained by use of an Ayre scraper can result in a false negative rate of as high as about 30%.
Methods for obtaining samples directly from the endocervical canal are shown in FIGS. 3 and 4. In the method of FIG. 3, the narrow forward end of a pipette 13 is inserted into the endocervical canal. Preferably the tip of the pipette is positioned at about the external os, but it is difficult to position the pipette precisely so that sometimes the tip of the pipette is inserted almost up to the internal os 14 as shown in FIG. 3. Suction is applied drawing mucus containing exfoliated cells into the lumen of the pipette. Published research suggests that carefully performed external os aspiration gives more reliable results than any other known single method. A problem, however, is that the endocervical epithelium, unlike squamous epithelium, is friable and prone to bleeding. Not only is bleeding worrisome to the physician and patient, but a sample containing a substantial amount of blood cannot be evaluated by the cytologist with confidence. Another problem is that the method of FIG. 3 more often should be performed by a physician, whereas the methods of FIGS. 1 and 2 can be performed by skilled paramedic technicians.
In the method of FIG. 4 the soft tip 15 of a saline-moistened cotton-tipped applicator 16 is inserted into the endocervical canal and rotated and moved in and out. While less traumatic than the method of FIG. 3, there still is a chance of endocervical mucosal injury and bleeding. Also, cells valuable for diagnostic purposes adhere in the interstices of the cotton fiber. Further, it is difficult to transfer the sample to a slide, and vigorously rubbing the cotton-tipped applicator on the slide distorts the cells making them difficult to evaluate.
Adherence of and damage to cells also is a problem with the methods of FIGS. 1 and 2 because most scrappers presently used are manufactured from thin strips of wood and cells become trapped in the pores and cracks in the wood. There also is a possibility of abrading the cervix with the irregular edge of a wood scraper which may reduce the reliability of any future colposcopic examination of the cervix.
Two or more of the above conventional methods can be performed in sequence on each patient. Prior research has demonstrated that the combination of prior art methods resulting in the lowest false negative rate, a rate as low as 2%, is the combination of the methods of FIGS. 2 and 3, that is, the combination of T-zone scraping and external os aspiration. In spite of experts' recommendations that this combination of methods be used, physicians continue to use suboptimal methods, possibly because of the difficulty of performing an external os aspiration. For example, in a recent survey only 3.1% of pathologists representing 675 cytology laboratories stated that a combined external os aspiration and T-zone scraping sample was a "type of routine gynecologic smear" received by their laboratories.
A major problem in obtaining Pap smears is that any cells that are allowed to dry before being fixed become distorted and impossible to evaluate. Under ideal circumstances a sample is transferred to a slide and fixed almost immediately, within seconds after being obtained. This problem is magnified when a combination of prior art methods is used because usually all of the separate samples are obtained and placed on a slide before any sample is fixed, with the result that at least some air drying occurs.
Slides received at a laboratory show significant variation, illustrating a wide range of sampling techniques and methods of transfering collected cell-containing material to a slide. Individual slides may have a single large blop, multiple streaks, globs or a small spot of material such that it is difficult to examine individual cells, making examination time consuming and sometimes inaccurate.
In addition, a substantial proportion of slides received by a laboratory must be classified as "unsatisfactory" because no diagnosis can be given due to an inadequate amount of cell-containing material and/or significant air drying artifact. The proportion of "unsatisfactory" slides varies widely; for example, in one research study involving ten clinics using the same method, T-zone scraping, only one-half of 1% of the slides from one clinic had to be labeled unsatisfactory, whereas 25.6% of the slides from another clinic had to be labeled unsatisfactory because of an inadequate quantity of well defined cells. In this case, the patient should be scheduled for an additional smear sample to be taken which, in effect, doubles the inconvenience to the patient, the work of the doctor or paramedic and the consequent expense. Also, the patient may be distressed from having been asked to return for an additional smear, regardless of the reassurances that she receives from the physician that an abnormality is unlikely.
Different instruments and methods have been proposed to solve one or more of the problems discussed above. For example, to reduce expense it has been proposed that a sample be obtained by the patient herself, such as by use of a specially designed tampon or a "vaginal irrigation" kit, and mailed directly to the medical laboratory. High false negative rates have been demonstrated for self-obtained samples and, accordingly, use of these methods has been discouraged.
One study, in an attempt to explain the high false negative rate when screening for cervical intraepithelial neoplasia, verified that high numbers of cells are trapped in cotton-tipped applicators and wooden scrapers, whereas relatively few cells are trapped in plastic instruments; yet use of plastic instruments has been discouraged because such instruments have been manufactured with thin scrapers having sharp edges that can lacerate or abrade the cervix.
Kohl in his U.S. Pat. No. Re. 27,915 disclosed a scraping instrument having a narrow, cylindrical aspiration pipette projecting forward from the scraping edge of the instrument for insertion into the endocervical canal. As the narrow projecting end of the pipette is inserted into the endocervical canal, the scraper and pipette pivot about a flexible shock-absorbing joint to align the axis of the pipette with the length of the canal. It still would be difficult to position the leading end of the Kohl pipette precisely, and for any patient whose T-zone is located at or inward of the external os, no T-zone scraping sample would be obtained because the T-zone, or part of it, would be engaged by only the smooth, cylindrical periphery of the aspiration pipette.